1. Field of the Invention
This invention pertains to an unlocking tool for opening a container and, more particularly, to an unlocking tool for a container housing a thermoluminescent dosimetry (TLD) badge for radiation dosimetry.
The law requires personnel who work in a radiation field, such as a nuclear power station, to carry a TLD badge for the purpose of monitoring radiation dose sustained by the personnel while they are in the field. The TLD badges must actually be worn by the personnel so that the badges will be exposed to the same amount and type of radiation. FIGS. 1 and 2 respectively show a container 1 for a TLD badge and the TLD badge 50 housed in the container 1. The container 1 is generally in the form of a thin rectangular box and, as shown in FIG. 1, has three trapezoidal tabs 2, 3 and 4: one on each of the lateral sides; and one on a longitudinal side. The tabs 2, 3 and 4 are provided with slots 5, 6 and 7 so that the container 1 can be conveniently worn by the personnel. Since those personnel usually carry an ID card, each slot is so dimensioned that an ID card strap for attaching the ID card onto a chest pocket can pass through the slot and suspend the container 1 from the ID card. Which slot is to be used for suspension of the container is sometimes at carrier's choice and sometimes specified by regulations peculiar to the radiation field where the carriers work.
As shown in FIG. 2, the TLD badge 50 consists of a case 51 and a rectangular TLD plate 52 inserted in the case 51. In the example shown in FIG. 2, the TLD plate 52 has four thermoluminescent (TL) elements 53 arranged along its length. Those elements 53 are made of a thermoluminescent material, such as CaSO.sub.4 or Li.sub.2 B.sub.4 O.sub.7, which stores radiation energy inside when exposed to radiation. The case 51 has four windows 54 of different thicknesses each located in a position corresponding to one of the TL elements 53. Thus, each TL element is covered by its own unique window which provides different radiation absorption thicknesses to allow estimation of radiation dose for various organs at risk. The badge 50 may be provided with a machine readable code to enable automatic identification of a person who wore the badge.
When entering a radiation field, each person is given the container 1 with the TLD badge 50 in it. They wear the containers 1 while in the field and give the containers 1 back when leaving the field. The containers 1 are thereafter collected in one place where they are opened to remove the TLD badges 50. The removed TLD badges are then processed by a TLD reader for dosimetry reading. FIG. 3 shows such a TLD reader.
When heated by a tungsten lamp 55, the TL elements 53 emit light at an intensity and for an interval of time correlatable to the amount of radiation sensed by the elements. A photo multiplier tube 56 detects the illumination from the TL elements 53 and transmits an electrical signal to a readout device of the TLD reader.
2. Description of the Related Art
Turning back to the container 1, FIG. 4 is a cross sectional view showing the container 1 in the closed position, and FIG. 5 is a perspective view showing the container 1 in an open position. As mentioned above, the container 1 is generally in the form of a thin rectangular box made of a plastic and includes top and bottom halves 8 and 9. The top and bottom halves 8 and 9 are connected at their longitudinal ends 8a and 9a by a hinge 10 for rotation with respect to each other. The halves 8 and 9 are rotated around the hinge 10 and closed along their respective edges to form therebetween a space for accommodating the TLD badge 50.
The top half 8 has tabs 3a and 4a on its lateral sides 8b and 8c. Similarly, the bottom half 9 has tabs 3b and 4b on its lateral sides 9b and 9c. In addition, the bottom half 9 has the trapezoidal tab 2 on its longitudinal side 9d. When the container 1 is closed, the tabs 3a and 3b are joined to form the trapezoidal tab 3 in FIG. 1. The tabs 4a and 4b likewise form the trapezoidal tab 4 in the FIG. 1 when the container 1 is closed. When the container 1 is closed, it is sealed by an annular rubber seal 11.
The container 1 is equipped with a locking mechanism to keep itself closed. Specifically, the top half 8 has on a longitudinal side 8d a latch finger 12 extending perpendicularly to the plane dividing the container 1 into the top and bottom halves 8 and 9. As shown in FIG. 4, the latch finger 12 has a wedge-shaped end portion including a slant surface 12a and a holding edge 12b. On the other hand, the tab 2 of the bottom half 9 is provided with a smaller slot 13 adjacent to the slot 5. When the container 1 is being closed, the latch finger 12 passes through the slot 13 and engages therewith to lock up the halves 8 and 9 together.
To facilitate a description and understanding of the invention disclosed here, the locking mechanism is described in detail. When the container 1 is being closed, the slant surface 12a of the latch finger 12 first comes in contact with the periphery of the slot 13. The top and bottom halves 8 and 9 are then pressed against each other. As the halves 8 and 9 are pressed against each other, the latch finger 12 is bent towards the hinge 10 and advances into the slot 13. At the same time, the periphery of that slot 13, keeping in contact with the slant surface 12a, is moving up on the surface 12a towards the holding edge 12b. At that point in time when the slot 13 reaches the holding edge 12b, the latch finger 12 snaps back to the perpendicular position, so that the holding edge 12b catches the slot 13. Once the container 1 is closed, the top and bottom halves are locked up together by the engagement between the holding edge 12b and the slot 13. To open the container 1, the latch finger 12 must be bent to release the engagement between the holding edge 12b and the slot 13.
The above engagement between the holding edge 12b and the slot 13 must be very tight to keep the container 1 closed against various unintended external forces, such as a drop impact exerted when the container 1 falls off to the ground accidentally. If the container 1 opens while in use, radiation dosimetry is no longer accurate. To prevent the container 1 from opening by accident, the latch finger 12 is formed very stiff and cannot be bent easily. Therefore, a special unlocking tool is necessary to release the engagement between the holding edge 12b and the slot 13 in order to open the container 1.
FIG. 6 shows one of the prior art tools which has been used for opening the container 1. As shown in FIG. 6, the tool is a rectangular plate 20 having a pushing finger 21 and a deep notch 22 adjacent to the pushing finger 21. In use, an operator holds the container 1 in one hand and the tool 20 in the other hand and inserts the tab 2 of the container 1 into the deep notch 22 as shown in FIG. 7 until the pushing finger 21 abuts against the slant surface 12a of the latch finger 12. The operator then pushes the tool 20 against the container 1. When the tool 20 is pushed against the container 1, the pushing finger 21 pushes the slant surface 12a and thus bends the latch finger 12 towards the hinge 10, thereby releasing the engagement between the holding edge 12b and the slot 13.
But the actual use of this tool 20 is not so easy as it appears to be. First of all, an intensive force is required to bend the stiff latch finger 12 when the tool 20 is pushed against the container 1. Since one operator usually has to open hundreds of the containers 1 during a work shift, he could not complete his job without hurting his hands unless he protects his hands with special gloves. Also, the use of the tool 20 requires special skills. The pushing finger 21, when pushed against the slant surface 12a, tends to slip up along the surface 12a and cannot effectively push the surface. The operator therefore has to push the tool 20 against the container 1 without causing any relative movement between the pushing finger 21 and the slant surface 12a.
FIG. 8 shows prior art of another type which has been used to open the container 1. In FIG. 8, an unlocking tool 30 includes two identical plates 31 and 32 each having the shape of the letter "C". These two plates 31 and 32 are secured to each other by bolts 33 with a space between them. The space between the plates 31 and 32 is slightly wider than the thickness of the tabs 3 and 4 of the container 1. The distance D between the arms of each plate is slightly wider than the width W, shown in FIG. 1, of the container 1. The plate 31 has a bolt 34 screwed at the center of its yoke. The head of the bolt 34 (not shown) is located between the plates 31 and 32. The plate 32 is provided at the center of the yoke with a projection 32a extending in parallel to the arms of the plate 32. As shown in FIG. 8, the projection 32a is inclined over an angle with respect to the plate 32. In use, an operator inserts the container 1 between the arms of the tool 30. The tabs 3 and 4 of the container 1 are also inserted between the plates 31 and 32. The container 1 is inserted until the slant surface 12a of the latch finger 12 abuts against the projection 32a. The operator then pushes the container 1 against the tool 30. When pushed against the slant surface 12a, the projection 32a pushes and bends the latch finger 12, thereby releasing the engagement between the holding edge 12b and the slot 13.
The tool 30 is easier to use than the tool 20 discussed above because the operator does not have to worry about positioning of the container 1 with respect to the tool 30. The lateral movement of the container 1 is restricted by the arms of the tool. Vertical movement of the container 1 is also restricted because the tabs 3 and 4 are located between the plates 31 and 32. In addition, when the projection 32a abuts against the slant surface 12a, the tab 2 of the container 1 comes right under the head of the bolt 34. When the container 1 is pushed against the tool 30, the head of the bolt 34 abuts against the tab 2 and restricts the latch finger 12 from moving upward and away from the projection 32a. However, the tool 30 still requires on intensive force to bend the stiff latch finger 12 when the container 1 is pushed against the tool 30.